“There is a train that is derailed and it’s on the northern side of Veterans Street on the rail track there adjacent to the chip piles,” Lyons said.

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The engine didn’t derail, just some boxcars that he said were empty.

“I’m not sure if it was an inbound or an outbound that actually derailed,” he said.

The incident, which happened at about 10 a.m., involved three empty boxcars, Cynthia Scarano, Pan Am vice president, said early Tuesday afternoon in North Billerica, Mass.

“They were just switching in the yard, so they’re all upright, in line, so we’re expecting them back on very quickly,” she said of the boxcars.

Scarano said Pan Am officials haven’t yet determined what caused the derailment or whether there was any damage.

As Pan Am officials worked to get the boxcars back on the rails, red lights at the nearby rail crossing on Veterans Street continued to flash, causing confusion among several drivers crossing the yard from Routes 2 and 108.

“Whenever there is a train there, it activates the crossing lights,” Lyons said.

Traffic, whether cars or commercial trucks and logging trucks, stops at the crossing as usual when the signal is flashing.

Drivers looked both ways and most proceeded across when they realized no train was coming.